Streptomyces is well-known for the production of structurally diverse natural products, including many industrially important bioactive molecules, such as oxytetracycline, chloramphenicol and bleomycin. Most of these bacterial secondary metabolites are produced by complex biosynthetic pathways encoded by physically clustered genes. Among characterized biosynthetic enzymes, polyketide synthases (PKSs) and non-ribosomal peptide synthetases (NRPSs) are most commonly observed. The blue pigment indigoidine [5,5′-diamino-4,4′-dihydroxy-3,3′-diazadiphenoguinone-(2,2′)] was previously isolated from phytopathogenic Erwinia and other bacteria. It may be synthesized by condensation of two units of L-glutamine by a 4′-phosphopantetheinyl transferase (PPTase)-activated NRPS, such as IndC from Erwinia chrysanthemi and Streptomyces aureofaciens CCM 3239 and BpsA from Streptomyces lavendulae. Because of the presence in its structure of carbon-carbon double bonds conjugated with a carbonyl group, indigoidine is a powerful radical scavenger that enables phytopathogens to tolerate oxidative stress, organic peroxides and superoxides during the plant defense response. Recently, indigoidine has also been found to possess antimicrobial activity.
Streptomyces chromofuscus ATCC 49982 was previously isolated from soil collected from a stand of mixed woods from the Stepping Stone Falls Beach Pond State Park, R.I., USA.
Unfortunately, despite its various utilities, conventional methods for production of indigoidine provide for only limited production, which may limit the industrial use of this promising compound. Mere optimization of conventional methods is unlikely to provide meaningful increases in the production of indigoidine.